It is necessary to control axial rotation of a rotational drive source such as a motor over multiple rotations in order to control positions of machine tools or mobile bodies such as robots. In particular, it is extremely important to detect angles within one rotation at high resolution and obtain angle information over a larger number of rotations. However, a large number of rotation angle detection apparatus with increased resolution as well as with angle information for an increased number of rotations have been proposed conventionally.
To deal with the problems of increases in the number of angle detectors, complication of a gear mechanism, and increases in the size of the gear mechanism when using two angle detectors differing in a shaft angle multiplier for angle detection of one axis in order to increase detection resolution within one rotation and increase a multi-turn detection range, an absolute position detection method disclosed in Japanese Patent No. 3665732 proposes a method which quadruples the resolution without decreasing the multi-turn detection range and without increasing the number of resolvers by using a 4-fold angle resolver for a first axis and a 1-fold angle resolver for a second axis.